In recent years, in response to the new National Environmental Air quality Standard, the Beijing, Tianjin and Hebei surrounding areas have put forward specific requirements for iron and steel enterprises to control fine particulate matter pollution in response to the requirements of PM2.5 control standards. From January 1, 2015, Beijing, Tianjin and Hebei regions have put forward specific requirements for the control of fine particulate matter pollution. The new emission standards and special emission limits for various production processes in the iron and steel industry formulated by the State began to be implemented, in which the emission concentration of gas pollutants was reduced to 10 mg / m ~ (3) or 20 mg / m ~ (3). On the basis of improving environmental protection facilities and enhancing the collecting capacity of dust removal facilities, The filter material of the ordinary bag filter used extensively by the enterprises can no longer meet the discharge requirements. According to the fan configuration of the dust removal condition in each process of iron and steel, replacing the ordinary filter material with the membrane filter material can further reduce the pollutant emission concentration. Meet emission standards.

PTFE microporous membrane is used to heat melt to the surface of the common filter material to form a surface filtration layer. The experimental data show that the membrane coated filter material has a significant protective effect on the original filter material, and the resistance of the system can be reduced by about 50% for a long period of time. The service life can be more than 3 years, the emission concentration can be controlled stably below 10mg/m3, and the zero emission control of PM2.5 can be basically realized.

Development of Dust removal filter Media in China

Bag dust removal came into our market in the 1950s. In the absence of domestic special dust removal filter material, the first use is wool felt, cotton cloth and other civilian fabrics. The first brand of domestic filter material-208 industrial polyester flannel was developed in China. In 1978, the three-dimensional needle-felt filter material was successfully developed to meet the needs of high-energy pulse ash cleaning bag filter, thus making the structure of dust removal filter material break through from two-dimensional to three-dimensional. In 1985, 729 cylindrical satin woven filter material was successfully developed to meet the needs of backblow bag filter. Furthermore, MP922 high strength antistatic filter material was developed successfully in 1990's, and PTFE membrane filter material was successfully developed in 1994. The filtration mechanism of dust removal media was changed from bulk filtration to surface filtration. Especially for the viscous ultrafine dust, the filtration efficiency is increased by an order of magnitude, and the running resistance is low and stable.

Since the 21st century, with the bag dust collector entering new fields such as utility boiler and garbage incinerator, the collected flue gas has the characteristics of high temperature, high concentration, high humidity, strong corrosion and variety. The filtration function is also extended from the removal of particulate matter to the removal of fine particles and purification of harmful gases. Therefore, higher requirements have been put forward for the function, variety and quality of dust removal media. In the process of practice, the chemical and physical properties of the filter media are improved to a certain extent, the efficiency of the filter media is improved, and the use time of the filter material is prolonged. With the development of nanometer environmental protection technology, the development of nanoscale environmental protection technology is gradually accelerated. In the process of making filter media, nanometer technology is gradually used to decompose harmful and discarded gases by using nano-catalyst airflow netting technology.

Of course, compared with the developed countries, there are still many problems in our filter industry, such as the overall equipment level is not high, low level repeated construction uneven in quality products, production line, chemical fiber high temperature dependence on imported raw materials, postprocessing process is weak, but in the country to vigorously promote the opportunity of PM2.5 control, bag as will be an important means of air pollution control to high-speed development.

Main Dust removal filter Media suitable for Iron and Steel Kiln

Among all kinds of filter materials, the filter material suitable for iron and steel furnace is divided into normal temperature filter media and high temperature filter material. Among them, the normal temperature filter material mainly includes polyester needle felt and acrylic needle filter felt. The high temperature filter material mainly has Metasmex METAMAX acupuncture felt, glass fiber needle felt and so on.

The filter material is woven with polyester staple fiber as raw material. It has the characteristics of high strength, low elongation, strong acid and weak alkali resistance, and its service life is generally 4 times or 6 times that of fiberglass fabric. It has good air permeability. The dust collection rate is high, the dust removal rate is easy, and the dust removal efficiency can exceed 98.99. The filter material is used most frequently in the collection of atmospheric flue gas of dust catcher in iron and steel furnace.

Acrylic acrylonitrile felt filter media. The filter material is a synthetic fiber filter material with good hydrolytic resistance and suitable for continuous operating temperature of 125 ℃ to 140 ℃. The filter media is suitable for organic solvents, oxidants, oxidants, etc. Inorganic acids and organic acids have good resistance to hydrolysis, but generally alkaline resistance, in the iron and steel furnace non-alkaline environment and high moisture content, easy to produce oil fog pollution environment can be used.

Metas Needle felt filter material. The filter material is made of Nomax fiber, has excellent temperature resistance, can be operated continuously at 204 ℃, and has good chemical resistance, Low concentrations of acids and bases and most hydrocarbons have no effect on it, and even a small amount of fluoride does not cause significant corrosion; it has outstanding high temperature stability. The thermal shrinkage is less than 1 at 250 ℃, the decomposition and carbonation only begin at 400 ℃ with excellent fire resistance, the limiting oxygen index is 30 points, neither spontaneous combustion nor combustion support is achieved. The filter material is widely used in various high temperature flue gas filtration occasions.

The filter material is a kind of flame-retardant, heat-resistant and stable fiber filter material, which can withstand temperature up to 260 ℃. The filter material is mainly used for dry dust removal of blast furnace gas.

Glass fiber needle felt filter material. The filter material is made of unordered interlaced fiberglass monofilament, with no directional three-dimensional microporous structure, small void, large void law, good sound absorption, shock absorption, corrosion resistance, insulation, and high temperature resistance. The filter material has the advantages of high porosity, low gas filtration resistance, high filtration speed, high dust removal efficiency, bending resistance, wear resistance and stable size. It is used for high temperature flue gas capture in iron and steel furnaces.

PTFE filter media. The filter material has non-viscosity, heat resistance of 240 ℃ to 260 ℃ can be used continuously, sliding (lower friction coefficient, moisture resistance (surface non-water and oil, wear resistance, corrosion resistance, It is mainly used to cover the surface of all kinds of dust removal filter media to increase the filter precision and environmental adaptability of the dust-removing cloth bag.

At present, the dust bag filter material mainly used in iron and steel industry is the first five kinds of filter media mentioned above, which are used for dust removal at room temperature, secondary capture and dust removal by high temperature flue gas, respectively.

Selection of filter Media in different processes

Different working conditions exist in different working procedures of iron and steel enterprises , so there are also differences in the selection of filter materials .

Coking. The temperature of coking flue gas is about 90 ℃, the instantaneous temperature can reach 130 ℃, the flue gas contains less sulfur and less moisture. According to the different parts of the process, the performance requirements of filter bag are also different. For example, coke and dust removal requires anti-static, flame-retardant, The coke table and dry quenching dust removal require anti-static, and the screening coke and dust removal require waterproof, oil-proof and anti-static. After years of application, it has been proved that using PTFE coated polyester needle felt as filter bag can meet the requirements of flue gas capture in performance. At the same time, the emission concentration of particulate matter is basically controlled at 10 mg / m ³ or 20 mg / m ³, which can meet the new emission standard and special emission limit.

Sintering. The flue gas at the head of the sintering machine is generally equipped with dry, semi-dry and wet desulfurization systems after electrical dedusting, in which bag dust removal is required after the semi-dry desulphurization system. According to the flue gas temperature of the sinter head after desulphurization (about 90 ℃) and the composition (a small amount of SO2、NOX, dust), the bag dust removal with PTFE coated polyester needle felt as filter bag can effectively guarantee the discharge according to the standard.

In order to meet the requirement of special emission limit value (20mg/m ³), electric dust collection can be changed to cloth bag dust removal. According to the concentration analysis of bag dust removal used by sintered fuel, the fume is collected by electric precipitator, flux, batching, and whole particle dust remover at present, in order to meet the requirement of special emission limit value (20mg/m ³), the electric dust collection can be changed into cloth bag dust removal. Using PTFE film-coated polyester needle felt as filter bag, the discharge concentration can be kept around 10mg/m ³.

Blast furnace ironmaking. According to the characteristics of blast furnace flue gas, all blast furnace flue gas environment dust removal is waterproof, oil-proof PTFE film coated polyester needle felt as filter bag, particulate emission concentration can be basically controlled within 10mg/m3, The main composition of blast furnace gas is, CO、CO2、N2、H2、CH4， of which the combustible component CO accounts for about 25%. At present, dry dust removal is used to purify it because the flue gas temperature of continuous operation is above 200 ℃. The high temperature resistant glass fiber or P84 (polyimide) must be used as filter material. However, after practical use, the glass fiber filter material is easy to break, and its life is short, and the filtration accuracy cannot be guaranteed for a long time. Instead, the PTFE coated membrane P84 (imported from Austria) needle-punched filter material is used. Under normal conditions, the service life can be up to 3 years, and the emission concentration of particulate matter can be controlled stably at about 3mg/m ³, which can completely meet the needs of production.

Electric furnace. At present, the dust removal of electric furnace adopts a three-stage capture method with four holes, a dog's kennel and a roof cover, which reasonably mixes the high temperature flue gas with the room temperature flue gas, which effectively reduces the inlet flue gas temperature of the dust collector. But considering the sudden situation, The temperature of flue gas may reach more than 200 ℃ in the instant. Therefore, using PTFE coated Metas filter material can not only reduce the operating cost, but also effectively capture flue gas, filter efficiently, and ensure that the concentration of particulate matter emission is controlled below 10mg/m3. Of course, In the field application, there is a short pipe between the trap cover opening and the dust collector entrance caused by space restriction, and the high temperature flue gas will enter the dust collector in a short time, and a large number of dust removal bags will be burned out. At this time, This kind of accident can be avoided effectively by using glass fiber filter material in the dust collector.

The secondary flue gas of converter belongs to the range of normal temperature. Using PTFE coated polyester needle felt as filter bag, the discharge concentration can be kept around 10mg/m3, which can meet the requirements of the latest particulate emission concentration.

The refining process of AOD.AOD belongs to the reduction reaction process. If the flue gas from the furnace and the flue gas from the roof are collected separately, because of the high temperature and alkalinity of the flue gas of the furnace body and the leakage of the water-cooled flue gas, etc. The selected filter material must have the characteristics of waterproofing and alkalinity resistance. It can be selected as PTFE coated Meitas filter material, which can not only be waterproof, but also has the characteristics of resistance to alkali and high temperature. The dust removal of roof cover is made of PTFE coated polyester needle felt as filter bag. It can meet the requirements of collecting and discharging. If a dust collector is used after mixing the flue gas from the furnace body and the roof, the inlet flue gas temperature of the dust collector can meet the requirements of the room temperature because of the mixing effect of the smoke from the roof at room temperature. Therefore, PTFE coated polyester needle felt can be used as filter bag.

Other environmental dust removal. Generally in the case of drying and flue gas temperature below 100 ℃, the filter material of environmental dust collector is made of PTFE coated polyester needle felt as filter bag.